Industrial processes for producing polyurethane foam, especially rigid polyurethane foam, include injecting polyols and multi functional isocyanates with curing and blowing agents by using a twin injection nozzle. This nozzle and the inside of the nozzle pipe are cleaned immediately after each operation to prevent clogging by cross-linked polyurethane onto the nozzle and pipe surface. Chlorinated solvents or hydrocarbon solvents are commonly used in this cleaning. However during their use, gel solutions are formed due to cross linking reactions between the polyols and multi functional isocyanates in solution. Such gel solutions can not be recycled for reuse.
It is well known that alcohols, especially primary alcohols, are useful to prevent gel formation in such solvents. In rigid polyurethane foam applications, the (—OH) portion of the alcohols easily reacts with excess isocyanates (—NCO) and, thus, prevents the cross-linking reaction from occurring. However most formulation comprising such alcohols have low flash points and thus are undesirable for use in factory settings.
Cleaning solvents categorized as non-DG (no flash point) that can remove rigid polyurethane foam on injection nozzles without gel formation in the solution are commercially available. Methylene chloride is commonly used in such solvents, but used solvent must be disposed of.
Therefore, a need exists for solvent systems suitable for removing rigid polyurethane foam from processing equipment, which solvent systems provide good solvency and non-gel byproducts, are suitable for recycle/reuse, and are otherwise suitable for industrial use.